Directional beamed radiant heaters



Feb. 3, 1970 M. lam-m 3,492,986

DIRECTIONAL BEAMED RADIANT HEATERS Original Filed Dec. 31, 1963 FIG. 2;

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INVENTOR Maurice Pcrfiof -M -m P ATTORNEYS United States Patent 3,492,986 DIRECTIONAL BEAMED RADIANT HEATERS Maurice Partiot, 12 Rue der Plateau St. Antoinette, Le Chesnay, France Continuation of application Ser. No. 334,842, Dec. 31, 1963. This application Apr. 18, 1966, Ser. No. 549,121 Int. Cl. F24c 3/04; F23d 13/12 US. Cl. 126-92 2 Claims ABSTRACT OF THE DISCLOSURE A ceramic plate for an infrared burner having a myriad of through passages for conducting a combustible gas mixture to a combustion surface of the plate. A combustion surface is provided with an indented surface which provides a greater intensity of radiation along one axis of symmetry of the plate than it does along another axis at right angles to the first axis.

This application is a continuation of US. application Ser. No. 334,842, filed Dec. 31, 1963, now abandoned and concerns radiant ceramic blocks and, in particular, the arrangement of passages therethrough for conducting the gas mixture, and burners with means for gathering and directing the infra-red radiation issuing from said blocks into an infra-red beam having a substantial percentage of approximately parallel rays.

It has been proposed in the past to feed an air and gas mixture through passages in said blocks and to burn it at the surface of a ceramic block of low heat conductivity, so that when said block heats up it becomes emissive of heat radiation as the combustion penetrates to a depth of about one millimeter inside the passages or perforations made in the block to supply combustible mixture to the radiant surfaces.

Examples of such blocks are to be found in the British patent to McCourt, No. 6312 of 1915, in which cylindrical passages are perforated through a refractory medium such as has been well known in the refractory art. In the British patent to Wilson, No. 25,714 of 1912, is disclosed a perforated slab or disc of convenient size or shape, made from fire clay, asbestos, or fire clay and asbestos substance or other suitable non-conducting refractory material. Later disclosures such as Schwank US. Patent No. 2,775,294, recite anew the techniques and limitations disclosed in the above patent as well as described in the prior art, but Which are especially directed towards extreme low heat conductivity outside the usual refractory ceramic range, with correspondingly low mechanical characteristics.

The Wilson design shows a cavity Or retort pattern in which a cylindrical passage is cut squarely across the bottom surface of the cavity, and a plurality of cavities is distributed evenly over the surface of the radiant block. When one attempts to construct the Wilson slab it is found that the square distribution and shape of the cavities and the wall strength required between cavities limits the aggregate area of the through passages to about twenty or twenty-five percent of the total radiant outside superficies of the outside slab.

It is an object of the present invention to provide a pattern of holes or cavities which allow as much as forty percent or more of aggregate passage area while retaining adequate mechanical resistance, a greater exchange surface for the combustion gases to be in contact with the ceramic, and a greater angle of dispersion over an area of ceramic material from which heat can be radiated in outer space.

To that effect, I provide in a number of combinations one or several of the following features:

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(1) A hexagonal distribution of the passages in honeycomb style, so as to crowd the said passages into the minimum area, and optional hexagonal indentations.

(2) A repeated cavity pattern regularly distributed over all the slab, each cavity arrangement receiving gas flow from a plurality to as many as eight adjacent passages or more.

(3) A slot connecting the outer end of the passages and cutting the passages at an acute angle to their axes, for a depth below the surface of more than one diameter of each individual passage. The slots or cavities in the face of the block are distributed regularly over the surface, and those portions of the face which are unslotted may be designated as areal surfaces from which radiant energy is emitted generally parallel to the direction of the axes of the two passages. Similarly, the bottom surfaces of such slots or cavities may also comprise areal surfaces which are substantially parallel to the surface of the block and from which also radiant energy is emitted generally parallel to the axes of the passages. Slanted surfaces joint the said areal surfaces at different levels of the block surface, and such slanted surfaces are the source of infra-red radiant energy which is emitted in a generally crosswise direction. Moreover, the interior of each passage which opens into such slanted surface provides a radiant surface which also produces a crosswise component of radiant energy. The secondary, or crosswise radiation, may be enhanced by selection of the shapes and sizes of the slots or cavities and may, if desired, by suitable design of the slots 0r cavities, be arranged to provide a symmetrical non-circular, but oval-shaped pattern of radiation intensity which is elongated in a direction parallel to one of the two principal edges of the block surface. If desired, a reflector may be disposed so as to have such enhanced radiation impinge thereupon and be reflected therefrom in a desired direction.

(4) A number of fins within each cavity formed by the Walls separating two adjacent passages, so as to provide in a single manufacturing operation the maximum heat exchange surface.

(5) A slot construction which cuts through the wall separating two rows of passages and which may be positioned to out only one single row of passages.

(6) In an embodiment of the invention, I provide an asymmetrical exhaust port for gas flow during combustion which causes the flame coming out of one passage to strike the fin placed just at the opposite side of the cavity.

(7) By providing a cavity design involving more than one row of passages, the outer uncut walls of the through passages are caused to radiate at a very high rate. This radiant heat exchange upgrades the temperature and intensity because of reverberation or mutual reflection of each side of the cavity to the other. The radiation level is built up within the said cavity before radiation to the outer space takes place.

(8) The effect of variation of gas pressure on the radiant efficiency of my device is less critical because the gas flame, regardless of its length or intensity, remains in contact with at least one substantial part of the fins or of the passage wall surface at its radiant outlet.

(9) In some embodiments, a hexagonal or square, or round, or a lozenge or trapezoidal form of the cavity is chosen for tooling purposes, and an asymmetrical pattern of gas flow during discharges from said passages into the said cavities causes a whirling sweeping motion of the gas within each of the cavities which increases the heat interchange between the burnt gases and the ceramic fins or walls.

The cavities, indentations or the like, or the intervening raised areas, can be square, oblong or triangular, lozenge circular, hexagonal or a succession of alternating parallel grooves and ridges and including long passages whose outlets are substantially entirely in said raised areas, or in a crisscross pattern of parallel grooves and ridges continuous or not, the relief differentials in the depth of indentations being preselected to favor one or the other of the straight out or the cross plate radiations.

The cavities may or may not be joined to each other by their slots, and my invention is not intended to be limited to isolated cavities as shown in the preferred embodiment.

The ceramic material comprising the block or slab according to one of the preferred forms of my invention is constructed of clay-type materials to which may be added materials having higher insulating properties or porosity than the clay itself, for retarding heat flow within the cavity or the block. Also, the structural strength of the block may be increased by suitable binders such as heatresistant pyrocerams or silicone compounds to prevent the walls between cavities from disintegrating after repeated heating and cooling cycles resulting from use. An equivalent result is obtained by using block material with a low relative coefficient of expansion and materials in the block mix which have substantially the same or closely related co-eflicients of expansion. Said mix may also include materials, well known in the art, for use in controlling to exact specifications the specific gravity, porosity, and heat conductivity of the block which has been fired in the kiln.

I also use surface means through painting or coating or through atomization of metallic droplets or of a high radiation material on the fins and walls of the cavities so as to increase their conductivity and heat exchange characteristics with combustion gases as well as their radiation efiiciency.

For special applications, a coating of cerium salts may be applied at the outer surface of the blocks along the walls of the cavities to obtain a substantial emission of light, or a coating of platinum salts or porous alumina or other substances of catalytic nature is spread so as to activate and complete the combustion of the gases.

The ceramic paste contains preferably very fine chamotte or grog (burnt fireclay), or exceptionally thermal isolant or finely ground charcoal, to improve the ceramics resistance to heat conduction rearwards of the block, provided the mechanical resistance and the resistance to heat-shock (i.e. expansion and retraction stresses) remain high. There is also available a very broad choice of porous or heat resistant materials some of which have either a steatite magnesia or zirconium oxide base, or any other refractory of higher characteristics may be used provided that it has a suitable resistance and strength.

The overall thickness of the block is preferably between one-fourth and five-eighths of an inch, thus affording a satisfactory barrier to backfire through the passages when operating under atmospheric injection by means of a Venturi-type injector as described in the McCourt patent.

My invention also includes greater thickness in devices where the air feed or the exhaust gases are accelerated by the means of a blower, so as to provide a greater area of heat exchange with the flame to heat said plate.

The ceramic blocks or slabs differ from the customary sintering of particles recommended in the prior art, by being completely baked at temepratures well above the service temperatures, and at about 2300 F. or over, for said clay-type materials.

Another feature of my invention consists in including the outer ends of the passages throughout the blocks or slabs as a part of the walls of the cavities, one portion of the circumference of a selected number of passages being at or near the radiant surface of the slab, and another portion of the circumference of the same passages being at or near the bottom of the cavity. This disposition does not exclude patterns in which substantially the whole perimeter of a number of passage outlets is located either at the outer radiant surface of the plate or at the cavity bottom.

A broad aspect of the invention consists in providing a great number of cavities of which the walls reflect heat to each other so as to upgrade their temperature and evacuate their excess heat through infra-red radiation towards outside space in front of the radiant slab.

The walls of the cavities may be preferably disposed so that a maximum of radiation emission from the cavity walls is directed along the short or the long axis of the slab to be gathered in an aluminum or metal, or a glass reflector, or in a pair of oppositely disposed reflectors, so as to direct the wall radiation towards the area to be heated by radiation.

The angles between said reflectors and between each reflector and the wall cavities may be made adjustable so as to concentrate the infra-red rays in a more limited area at various distances in the front of the radiant slab.

A more general feature of the invention consists in a multiplicity of passages in a fire-brick compound or similar refractory mixes in which a row of passages of which a number are split or opened up on one side along their exhaust ends, so that the outer end walls of said passages are heated up by the combustion of flame starting at the break off point of the passages and the radiation of said heated walls occurring crosswise of said passages is gathered in a reflector so as to be sent in the general direction of the initial flow of gases within said passages towards the area to be heated.

A further feature of the invention is to shift periodically the direction of the radiant rays from one area directly in front of the heater to areas to the right or the left of same, the purpose being that the physiological feel of heat is greater from periodical trains of heat radiation than from a steady one.

Such feature obtains through a greater concentration of heat in a burner, a far greater heat-sensing effect upon people in each of the areas including marginal areas than would otherwise be possible from a widespread radiation. For instance, a larger number of people gathered in the broad front of an oscillating burner can remain closer to the burner and feel a greater heating effect by periodic heating than if the rays were not first concentrated by reflectors but were spread evenly over all of them.

The effect of periodic heating will be obtained by the means of reflecting in variable directions the rays issuing from the ceramic Wall by the means of a periodic adjustment of the reflectors angles as compared to said walls; or by moving the heater and reflector assembly around its support and gas supply in a periodic manner, such as is done with an electric fan, or by other means.

Referring to the drawings:

FIGURE 1 shows a fragmentary plan view of a corner of a radiant slab, and the detail design of one retort or cavity surrounded by a repeat pattern of the detail design.

FIGURE 2 shows a section from left to right of FIG- URE 1. The right-hand side of FIGURE 2 shows a means outside the radiant slab for retaining the gases in contact with the outer radiant ceramic surface. The gas-retaining device made of a refractory material either metal or preferably silica glass or a combination of both can be of a griddle-like or screen design, or of a loose Web nature, or of a mattress of more or less dense silica fibers which let the gases escape through it as well as it does the radiation issued from the ceramic block, said screen structure or mattress being supported so as to be located in the burnt gas layer well beyond the limits of the combustion zone which is confined Within said ceramic indentation reaches and immediately adjacent to the latter. The gas retaining device of FIGURE 2 acts also as a baflle helping to control the extent, scope and direction of the radiation. It is held closely over the outer surface of the ceramic and is preferably made, in this embodiment, of

thin refractory metal so as not to impede the radiations.

FIGURE 3 is the schematic cut-out of the combination of a hot radiant wall with a reflector.

FIGURE 4 is a schematic diagram of a system of concentration of heat rays into a restricted area and of a means for a periodic shifting of the rays from said area to other restricted areas. The field concentrating and restricting means comprises reflectors and at least one optional intermediate baffle or bafliing means.

FIGURES 5 and 6 show two ways of orientation of the cavity walls so that the principal radiation from said walls is across one or the other axis of a slab to facilitate the concentration of said heat rays through the use of end reflectors opposite to said walls.

FIGURE 7 graphically illustrates one relationship between heat conductivity and specific gravity in a typical alumina silicate refractory,

In FIGURE 2 is shown the preferred design of the slab with the intake or cold face of the slab at the bottom. The slot or plate is supported on a burner body member 10 having a gas inlet 11. The preferred gas mixture at 105% to 125% of air as compared to the ideal 100% air figure for theoretically perfect gas combustion, is fed by any of the usual methods into passages P. The gas ignites in the shaded zone BB. As indicated, zone BB experiences variation in depth and length in accordance with the gas feed pressure. The hot gases expand during combustion and are deflected sidewise, more particularly against fins F. When the gas pressure increases, the deflection velocity and impact on said fin increases as a function of the pressure, yet the flame is still effective to heat the interiors of the activities. By contrast, in the prior art McCourt and Schwank designs, the gas combustion flame has a tendency, when pressure increases, to burn outside the flat plate, well above its radiant level, and the heat therefrom is lost by convection.

The cavity design of FIGURE 2 provides for sidewise deflection of the hot gases. As a result, the fins F and the wall passages facing the fins radiate heat to each other and to the outer space at a vastly higher level even over a wide range of gas pressure values, thus increasing the efliciency of radiation in dependence upon the fourth power of the increase in temperature as compared to Zero absolute. As the amount of the aggregate passage crosssectional area increases with respect to the overall radiant plate area, the surfaces between the passages, both parallel to the plate area and at an angle to it as occurs in the slopes, diminishes proportionately. However, the radiation issuing from the ends of the passages increases as the aggregate perimeters of said passages increase. The loss in the first is more than compensated by the second provided one-half to about two-thirds of said perimeter is removed by the slant of the slopes so allowing ample release of the radiation issuing from said passage inner walls. In such a preferred construction the release of the combustion gases and of the inner wall radiation are in the same direction, so providing a transverse radiant component.

The radiation escaping from the top of the slab such as R1 and sidewise from the walls such as R2 dissipates through radiation the heat absorbed by surface exchange from the hot gases of the combustion. I therefore provide a ceramic mix which can absorb the heat from the flame so as to radiate it back and which is substantially more heat absorbent and heat conductive than the ceramic mixes recommended, disclosed or claimed in Wilson and especially in Schwank. Indeed, one of the important alternate features of my invention is to provide a ceramic mix which is sufficiently conductive for the heat to flow back to the bottoms of the indentations from the outermost portion of the surface (zone BB) where the focus of the combustion is located.

This application is a continuation-in-part of my prior copending application Ser. No. 240,704 filed Nov. 28,

6 1962, now U.S. Patent No. 3,179,157 issued Apr. 20, 1965, and is also a continuation-in-part of my prior copending application Ser. No. 36,767 filed June 17, 1960, now U.S. Patent No. 3,179,155 issued Apr. 20, 1965 and of my copending application 440,465 of Mar. 17, 1965 which is a division of the aforesaid 36,767.

The type of ceramic mix I use has been described or variously used for a great many years for refractory or heat resisting bricks, radiant baffles or other heat radiation dispensing firebrick articles. One of such disclosures in the prior art is found in the U.S. Patent No. 1,852,713 of Apr. 5, 1932 to James H. Gill. Other available mixes are adapted for a wide range of temperature and radiation requirements.

Contrary to the widely accepted theories of extremely low heat conductivity for radiant slabs I have found that a moderately low heat conductivity facilitates the cooling of the back face of the radiant slab by the incoming gaes and also enhances heat exchanges of said walls with the gases during their combustion, and with the radiation from the walls of the cavities in accordance with my invention.

Furthermore, I have found it highly impractical, if not impossible to build a deep cavity radiant surface with a clay-like binder too porous or loaded with too much extraneous materials such as asbestos. When the aggregate gas passage areas increase from about fifteen percent to forty percent, then the amount of porous or asbestos type inclusions must drop sharply in order to retain a reasonable mechanical resistance for the cavity walls, and so as to avoid spalling and a breakdown of the radiant surface.

Furthermore, when enough passages are crowded in the radiant slab to come near or above forty percent of the total surface, then the mechanical characteristics of the very thin cavity walls become all important, while a moderate increase in the density or heat conductivity works favorably for both the mechanical characteristics of the ceramic mix and for the heat exchanging and radiant properties. The hot cavity walls conduct the heat from the path of the flame down to the bottom of the cavities, as would any other semi-conductive ceramic part protruding into the path of a flame from its bottom. I therefore preferably use for durability and high radiant efficiency a deep cavity radiant slab having a range of specific gravities of preferably no less than about 1.2 up to about 1.8, with a heat conductivity preferably above 0.5 kilocal./hr./m. for a temperature gradient of 1 C. per meter for an aggregate of passage areas preferably of no less than thirty percent as compared to the overall radiant slab area.

The ranges which are indicated above shown very definitely the highly novel aspects of my invention as well in the ceramic mix composition for a radiant heat perforated slab, and in the cavity design and in the heat exchanger surfaces used for emission of infra-red radia tions, as well as in its moderate heat transmitting characteristics as compared to the radiant plate outlined in U.S. Patent No. 2,775,294 describing means for extreme low heat conductivities.

In the prior art of indented radiant ceramics and in my own, I have found it at times diificult under unforeseen combinations of drafts on the plate surface and broad variations in pressure feed of the gas mixture to maintain the focus of the greatest part of the combustion at the outlet levels of the shortest through passages opening at the bottom of the indentations.

This effect has been quite definite in my plates or when using other types of indented plates such as are described in the Belgian Patents No. 551,980 of Huisinga and No. 558,007 of Haegan Auer, particularly when the theory of low and extreme low ceramic conductivities, as expounded by the Schwank in Patent No. 2,755,294 and generally accepted by the infra-red trade for flat faced plates, is put into practice in combination with said patterned surface designs.

As is required by the increases in aggregate port areas percentage with respect to overall plate surface for overheating said plates so as to make them more radiant, a greater amount of combustible gas mixture is flowing through each square inch of plate surface, and the flame has still a greater tendency to burn outside the indentations particularly and the more when the plate is made of an extra low heat conductivity ceramic medium as is accepted and recommended in the prior art.

The flame burns then partly or totally outside the indentations when the ceramic heat conductivity is low or very low, and the benefits expected from the indented designs are dissipated because of unprevisible operating conditions.

When, as in the present application, the orientation and the shielding of the radiant plate change in a predetermined manner, then it is of utmost importance that the greatest part of the combustion be solidly anchored to the bottom of the indentations of the radiant plate, so that it may retain its highest operating efliciency under practically all of the conditions of the uses to which the burner is being submitted.

Therefore, one most important aspect of the invention is to provide the means to stabilize the flame of the combustion at the bottom of the cavities and partly within the outlets of the shortest of the through passages in said indented plate.

To that effect, a proper combination of conditions has to be devised to cause some of the heat absorbed by the contact of the flames of the combustion with the raised surfaces between two adjacent cavities or slots, to be controlled to feed back and heat the outlets of passages opening at least in part within said indentations.

As the plate is lighted, the raised intervening areas are becoming overheated and the heat absorbed by said raised areas is caused to flow back within the ceramic walls between adjacent passages to heat by conduction the areas remaining between the saids areas, thus raising considerably the temperature of said remaining areas.

A middle conductivity range of heat conductivity and ceramic porosity or specific gravity is used in combination with adequate restrictions in said wall cross-sections to channel and control back flow of heat from the overheated raised areas to the remaining areas separating said raised areas.

As the plate operative fully radiant condition is being reached, the differences of temperatures between the various levels of the plate are diminishing and the locus of combustion is firmly anchored within the passage outlets at their shorter ends, penetrating into said passages for a distance of about one diameter at most.

The control of the back flow of heat from the raised surfaces comprises as well such provisions in the nature of the ceramic of the whole plate including said raised areas, and in the dimensions of the walls intervening between adjacent passages so as to prevent the flow back of said heat to extend very much further than the bottom of the indentation lest the combustion of the mix start propagating further upstream towards the back face or first face of said plate. This is achieved by providing adequate development and cooling of the inner passage wall surfaces adjacent said first surface by the incoming gas mixture.

This particularly delicate balance in the heat flow and heat exchanges is more readily obtained within the heat conductivity and the specific gravity or porosity limits claimed and disclosed in the invention, in combination with a predetermined cross-section of the ceramic walls separating adjacent passages as compared to their diameter.

FIGURE 3 describes in more general terms the basic principle of the combustion of gases at the end of a refractory passage which is cut open along a part of its length so that the walls of the passage become heated by the combustion flame issuing at the beginning of said cut. The cavities or depressions 10 (see FIG. 1) are distributed regularly over the surface of the block or plate. The portions of the plate which do not have cavities therein may be considered as elevated elemental areas from which infra-red radiation is emitted in a direction generally parallel to the axes of the through passages 11. The bottom surfaces 12 of the cavities comprise elemental areas which are depressed relative to the non-cavitied portion, and these surfaces 12 are also the source of radiation which is directed outwardly generally parallel to the axes of the passages. The first and second elemental areas are joined by sloping or slanted surfaces 13 into which at least some of the passages open so as to form axially elongated peripheral openings, a portion of which is substantially raised relative to an opposing wall of the passage. By this means, a portion of each passage has its interior exposed so that the radiation therefrom is emitted freely and unimpeded transversely to the surface of the plate and in generally the same direction as the radiation emitted from the corresponding sloping surface. Thus, to the end radiation R1 is added a side radiation R2. The side Wall P1 and the fin F conducts heat back to the passage wall P1 to cause it to radiate at a faster rate.

The principal radiation R2 takes place crosswise to the axis of the passage. An adjustable reflector M is placed opposite the slot of the passage, many passages being located so that the inner walls of the split open passages cause a strong emission of cross radiations R2 to be received and reflected by a metal radiator such as aluminum, or by a glass radiator in a direction generally parallel to the axis of one of the passages.

The disposition of the intersected passages with respect to the cavity walls is such that the release of the cross plate radiant emission from the inner walls of said intersected passages is controlled by the extent of the side opening or gating resulting from the intersection of said passages with said surfaces. It can readily be seen in FIGURE 1 that the side opening and subsequent release of inner passage wall radiations is greater in the direction joining the apexes of the two obtuse angles positioned to be along one axis of the plate, than it is in the crosswise direction of the line joining the apexes of the two acute angles in the described lozenge form cavity.

Inasmuch as the extent of exposed inner wall surface of the passages and of the corresponding release of radiations from said exposed walls can be made to differ greatly so as to favor the emission of radiant emission towards a reflector located at two opposite edges of the plate to receive it, and minimize the release of radiations by narrower gating (FIGURE 2) in a cross direction, the plate is called directional and the burner generally requires reflectors but on two opposite sides, the two other edges of the plate having but mere baifles to protect it against cooling air currents.

In one embodiment of the invention the reflector M is adapted to swivel with respect to the radiant surface so that reflected radiation R3 can be added to radiation R1 at a variable distance ahead of the radiant passages.

In FIG. 2, the aggregate volume of the structures extending beyond the ceramic plate occupy less than 10% of the spatial volume defined between the ceramic plate surface and the plane tangent to the farthest extension of said structures beyond said plate. They are adapted to provide no substantial obstacle to the free flow of burnt gases and radiations, while the structure itself may be designed to enhance a directional effect in the plate design.

FIGURE 4 shows a radiant plate with cavities comprising a number of side-indented passages like those shown in FIGURE 3 and radiant walls opposed to each other within each cavity and radiating heat each to the 9 other, and the radiation R2 of FIGURE 2 escaping out of the cavity is gathered in FIGURE 4 by opposing reflectors M1 and M2 to be concentrated in a restricted area D.

In a further embodiment of my invention, the reflectors M1 and M2 are swiveled around a shaft by the means of a linkage guided and moved in an alternate fashion through a cam C.

As the reflectors M1 and M2 are moved simultaneously with or independently from the radiant surface, the radiations issued from the burner are directed alternately to areas D1 and D2 to the left end and the right end of area D. The axis of the rotation can be horizontal or vertical or slanted at an angle.

I have therefore observed that, when cooling with a swivel fan the cooling effect is physiologically greater than when the blast of the fan is continuous, so is the greater physiological heating effect of a periodic train of heat radiation waves as is described in my invention.

One means of intermittent radiant heating is shown in FIGURE 4. Another means consists of swiveling by a cam-like means or the like, the whole burner and reflector assembly around a fixed support.

In the usual stationary radiant burner, the heat is either too broad and it does not heat sufficiently, or it is too narrow, and it cannot heat but a few people in front of it and the heat becomes too great and needs to be turned down. My invention allows the heating in turn periodically of a larger area of people by the means of a sweeping concentrated beam of infrared radiations, with a greater effect, lesser actual heating of any one area, and lesser overall gas consumption. The burner can, however, be adjusted to stay for a period of time in any one of the range of its positions.

'It also has been observed that radiant overhead heating on workers in a plant shed or in a warehouse, unless the burners are placed very high, has a tendency to congest the head and the back of the neck. Such elevated burners lose a great part of their effectiveness and capacity because of their excessive distance from the heated locations.

In accordance with the invention, intermittent and cyclic heating is more efiicient since it can be used at closer ranges, principally because of the intervening cooling periods during which blood circulation takes away to other parts of the body the excess heat that may then be endured while the same area is being at least in part shielded from the radiation issued by the burner. The partial or complete shielding of areas immediately adjacent to the restricted field receiving a concentrated beam of radiations is one essential factor when the heater is used at shorter ranges than is the practice in order to take advantage of its higher heat impact properties and raise its efliciency. At the same time, the intermittent cyclic heating and alternating shielding periods allow the blood circulation in each one of a heated group of people to take the heat away to other parts of the body and avoid congestive effect on the bare parts of the body exposed to said enhanced heat.

Reflectors and field narrowing baffles extending to a substantial distance ahead of the radiant surface provide both a concentrated beaming of the radiant emission into a narrowed area, and at least in part the necessary shield against radiations for areas immediately adjacent said first-named one. (In addition, for enhancing the overall effect in a room or outdoors, the burner itself may be angularly pivoted from an overhead support to sweep very broad angles or be rotated to sweep areas located in a 360 angle around the vertical to its support. Adequate joints for gas feeding are known to meet the tightness requirements of a rotating pipe.

FIGURES 5 and 6 show two preferred dispositions of the cavities, with the walls of the cavities being generally directed along one or the other axis of the radiant slabs,

10 so that the principal radiation R2 can be gathered by refectors M as shown in FIGURE 3.

FIGURE 7 shows an approximate relationship between the heat conductivity of an average alumina silicate refractory mix with the specific gravities, which in turn are indicative of the porosity of the particular article of manufacture made out of the same refractories.

It is to be noted that considerable data are available to confirm the relationship of heat conductivity with specific gravity in the lighter refractories having a high porosity. One of said relationships is found in existing tables for chamotte stone specific gravity and in the curve corresponding to such clay-base materials.

The curve below 1.2 specific gravity corresponds for a clay base refractory to an average heat conductivity below .5 with a ten percent possible error or more on individual measurements. The area which concerns the invention is centered around .6 to .7 kilocal./hr./m. for a temperature gradient of 1 C. per meter heat conductivity which for clay base refractories means 1.4 to about 1.5 specific gravity for a material having the proper desired characteristics to carry out one embodiment of my invention. Heat conductivities lower than .5 can be used when a burnt gas blanket stagnator is adapted to cover a substantial part of the plate area.

It is to be noted that the curves vary substantially when the refractory base materials are changed, and a satisfactory structural strength can be retained for the formation of the wall cavities or of the refractory materials protruding above the bottom of said cavities. I could therefore use materials of acceptable durability having substantially lower specific gravity or lower heat conductivity although this may require greater care and skill in designing the extruded ridges and as is described at length in the Schwank 2,775,294 patent, would oppose and restrain the desired heat flow to the lower levels and to the bottoms of the indentations which for the stability of the combustion and the highest radiation efficiencies, must be maintained at a very high temperature so that the flame starts within the outlets of the shorter passages and settles there permanently during the span of operation of the heater.

It has been surmised by myself that the most advantageous aspect ratios and depths of indentations and of the more useful cavity or raised areas profiles designed for better heat exchange of the flame with the side walls, sloping or upstanding, do not work properly when the heat from the overheated raised portions is not permitted to flow backwards down to the bottoms of the indentations.

The Schwank ranges generally admitted as the best ones for flat face plates fail to satisfy the problems of indentation plate faces nor give them a proper solution. Thus, I clearly prefer for the indented plates of my inventions the higher heat conductivities and higher specific gravities which are rejected as undesirable for the flat plates of the Schwank patent.

As the amount of aggregate port area is increased and the thickness of walls intervening between two adjacent passages is decreased, while increasing the specific gravity by reduction of the ceramic porosity, I found that the amount of heat conduction backwards to the intake face of the plate had not substantially increased, because of reduced wall sections, and that such an increase was compensated by the larger cooling surfaces in the passages at the inlet face. The effect is quite evidenced when the aggregate port area is increased from 40% to 45% of the overall plate surface, and the backfiring propensities with petroleum base and natural gases are not very substantially increased under normal operating conditions.

In FIGURE 4, the upstanding walls of the indentations are substantially parallel to the axes of the passages and the indentations have a cross section extent and depth suitable to such purposes that are imposed by the requirements to which the burners are designed; the upstanding walls provide for an equal depth of the indentations a far greater extent of radiation surface than do the lazy slope profiles; furthermore, the indentations in FIGURE 4 comprise substantially more passages than the four passages of FIGURE 1. The shapes of the cavities may be of directional type or not, and are very varied according to the operating requirements to which the burners and heaters are being put. The slanted cut passages and the side split passages intersected by upstanding Walls can be interspersed with cross cut short passages not shown on the drawings or by a number of cross out long passages emerging at least for their greatest part at the extreme outer surface of the plate; for instance, FIGURE 1 shows seven of such long passages which may also be located in between the indentations.

In most of the embodiments of the invention, the indentations edges are limited by intersected passages, and when the slope is an upstanding wall substantially parallel in sections to the passage axes, the extent of radiating surface that is usable is the greatest, since the exposed inner walls of the intersected passage provide an average of about 50% more contact with the flames of the combustion and corresponding radiant surface than in the cavity wall portions which do not intersect any passage at all.

In such upstanding wall cavities or indentations, the number of passage rows in two perpendicular directions that are encompassed in the cavity span S is higher than two as it is shown in FIGURES 1 and 2. For instance, in FIGURE 1 span S comprises rows of passages P P P and crosswise in FIGURE 2 span S comprises staggered rows of passages P P P To such side intersected passages can be added interspersed short passages cut across by the cavity bottom, or long passages cut across the outer surface as are shown in FIGURE 1.

The upstanding indentation walls cause some of the passages opening for part of their sections at the bottom of the indentations, while substantially the balance of their sections opening at least in part at the terminal end of the outer surface, said outer surface could also be corrugated or carrying a design of its own.

When I try to work my own-designs with ceramics having the generally accepted .26 to .35 kilocal./hr./m. for a temperature gradient of 1 C. per meter Schwank-type conductivities, then I obtain a combustion which starts at about the B level and all the walls below B and the cavity bottoms are far colder than the fin terminal portions, whose aggregate surface extent is too far limited to be of service, although I obtain for such reduced top areas far higher temperatures than are obtainable from a flat plate of like very low conductivity.

When I use the top limit in the Schwank disclosure and range, for instance .50 kilocal./hr./rn. for a temperature gradient of 1 C. per meter conductivity, the combustion starts at the B level and the flame is jumpy. The heat gathered by fin F flows back but in an insufficient amount, being blocked by the excess porosity and heat restraining features of the ceramic medium; it takes a long time to stabilize the flame at the cavity bottom, as the heat flows back slowly to the cavity bottoms along path W Under such conditions of thin walls and low heat conductivities, the cavity bottom temperature is far too low to contribute more than a very minor portion of the total radiation; the flame gets unstable and in deeper cavities jumps out and back, creating a humming noise akin to that of an improperly mounted electric transformer. The cavity depth and design and the ceramic conductivity are not adapted one to the other and the cavity walls are only part-time heated, with a resulting lag in efficiency.

When my plates have a heat scale relative conductivity above .50 in the .55 to .75 kilocal./hr.m. C. meter range corresponding for certain types of ceramic materials which I now use, to specific gravities between about 1.2- 1.25 and 1.50 up to 1.80, then I find it far easier to establish the correct balance between the cavity aspect ratio and depth on one hand, and the heat conductivity that can get the most efficient radiation out of the particular design or reversely, the heat conductivity and the design that takes the best advantage of it. It must be said at this point that denser mixes of the same materials in the mix are somewhat less radiant, the radiation loss being a minor one.

In the above indicated range, the heat feedback flows along paths W and W deep in the body of the plate. Path W preheats the gas mix above the safety level L located at about 40% of the thickness of the plate with respect to its backface. This cold part is shown shaded in FIGURE 9.

The combination of the feedback heat W and the feedback preheating heat W causes the combustion within the passages to move upstream from the B level to the B level, at which point the flame is safely anchored at its most effective location for highest radiation efficiency.

Such advances in the radiant heating are of a considerable importance in the selection of heat conductivities entirely outside the Schwank range and open a limitless field of possibilities in the control of radiation generation and in infrared wave length selective predetermination.

Plates of conductivities higher than .75 kilocal./hr./m. for a temperature gradient of 1 C. per meter or specific gravities higher than about 1.55 are generally used for larger spans and greater mechanical resistance; they are usually thicker and the scope of surface designs is more limited. It can readily be seen that the higher heat conductivity ranges impose stricter limitation controls in order to avoid backfiring particularly in the top end of the range.

While there have been described above what are now believed to be the preferred forms of the invention, variations thereof will be obvious to those skilled in the art and all such changes and variations which fall within the spirit of the invention are intended to be covered by the generic terms in the appended claims, which are variably worded to that end. In particular all of the designs and dispositions disclosed in my above mentioned prior applications, their continuations and divisions or the equivalent of said disclosures are intended to operate in combination with the present invention.

I claim:

1. A directional beamed infra-red radiant gas heater comprising a burner element defining a chamber into which a combustible gas mixture is admitted,

said element supporting an oblong refractory ceramic plate having a myriad of minute-bore substantially straight elongate passages extending therethrough from a first surface of said plate which is exposed to the interior of said chamber to a second surface thereof where combustion takes place, said plate at said second surface being defined at least in part by slanted surfaces which are inclined at acute angles to the longitudinal axes of said through passages,

a plurality of said passages opening at least in part into said slanted surfaces,

said slanted surfaces limiting the periphery of distinct substantially separate indentations whose crossdimensions are larger in the direction of one longitudinal axis of said plate than in a generally perpendicular cross direction, said slanted surfaces intersecting in part at least some of said passages so as to effectively cut away a portion of the peripheral wall of the intersected passages and thereby leave effectively exposed the interior surface of a part of the remaining peripheral Wall defining said passages, said exposed interior surfaces generally facing and directing radiation inwardly toward the central portion of the respective indentation, said slanted intersecting surfaces exposing a greater cumulative interior surface area facing generally in said direction of said plate as opposed to that facing in said cross direction, the pattern of said slanted surfaces being substantially symmetrically positioned with respect to both cross directions of said plates so that the repeat pitch of said pattern encompasses at least three succive lines of said passages in each of said two said perpendicular directions,

said slanted surfaces and the corresponding intersected passages being so disposed relative to each other that infra-red energy emitted from a major portion of the cumulative area of said exposed interior passage surfaces together with said slanted surfaces is directed with a substantial component generally along said one direction and a lesser portion of said infra-red energy is directed with a substantial component along said cross direction of said plate,

and reflecting means so disposed as to have at least a portion of the infra-red energy from said major portion impinge thereon and be reflected therefrom with at least a substantial component parallel to the axes of said passages,

the combination of said slanted surfaces and said interior surfaces together with said reflecting means comprising a means coactive to direct ahead of said burner element a substantial part of the total radiation emitted by said plate in a narrow beam of substantially parallel rays.

2. An infra-red radiant heater comprising in combination a one-piece oblong ceramic plate having a first surface which is exposed to the combustible gas mixture under pressure and a second surface adjacent which combustion takes place,

as the result of the lower opposite passage wall and with a substantial component transverse to the surface of said plate,

said upstanding surfaces also emiting infra-red energy with a substantial component in substantially the same direction as and adding to the energy emitted from said passage interior walls,

said upstanding surfaces and the corresponding intersected passages being so disposed relative to each other that the infra-red energy emitted from a major portion of the cumulative area of said exposed interior passage surfaces together with said slanted surfaces is directed with a substantial component generally along a first axis of symmetry plate and only a minor portion thereof is directed with a substantial component along a second of said axes of symmetry.

and reflector means positioned to have said transverse radiation from said major portion impinge thereon and reflect the same in a predetermined direction ahead of said second surface of said plate, the combination of said slanted surfaces and said interior surfaces together with said reflecting means comprising a means coactive to direct ahead of said burner element a substantial part of the total radiation emitted by said plate in a narrow beam of substanitially parallel rays.

References Cited UNITED STATES PATENTS said plate having two perpendicular axes of symmetry,

said second surface being formed in part by first a d n5 second elemental areas at r pe i y difiefent levels 5 1 95 5 fi H 15 116 of said first surface and upstanding surfaces ch 2832331 4/1958 s 8 join said first and second elemental areas, said 41 4/1963 il elemental areas and upstanding surfaces defin- 3170504 2/1965 S 158 116 ing indentations that encompass at least three suc- 3179155 4/1965 P m-lmg cessive rows of passages in each of two cr ss 3179157 4/1 art-lot 158-116 directions, n 965 Partiot 158-116 a myriad of minute cross-section straight passages 40 g i which extend through said plate from said first suf- 3277948 10/1966 6 158 116 face to said second surface, at least some of said est 158-116 passages intersecting at least one of said upstanding FOREIGN PATENTS surfaces so that one peripheral portion of each pas- 4r 1 44 30 9 1 0 prance. sage intersecting at least in part said upstanding sur- 1,246,639 10/1960 France" face is substantially elevated relative to an opposing 167,876 8/1921 G t B it i peripheral portion, 916,831 1/ 1963 Great Britain.

the interior wall of each passage which opens into an upstanding surface being substantially parallel to the axes of said passages adjacent said elevated peripheral portions and comprising a source of infrared energy which emits said energy unimpeded,

FREDERICK L. MATTESON, JR., Primary Examiner HARRY B. RAMEY, Assistant Examiner US. Cl. X.R. 43l328 

